Portable radio communication device

ABSTRACT

A small-sized flat antenna mounted on a portable radio communication device is available for a narrow bandwidth, and the resonance frequency of the flat antenna varies due to interference between the flat antenna and surrounding dielectrics such as a housing and a human body. As a result, the transmission efficiency and reception sensitivity of the antenna have been impaired. A communicating section (constructed of a coaxial line or a microstrip line)is arranged in a portable radio communication device having a circularly polarized antenna for satellite communication, so that an appropriate distance is provided not only between a housing of the portable radio communication device and the antenna but also between a human body and the antenna.

FIELD OF THE INVENTION

The present invention relates to a portable radio communication devicehaving circularly polarized antennas effective for satellitecommunication.

BACKGROUND OF THE INVENTION

In mobile communication through portable radio communication devices(portable telephones) and the like, linearly polarized waves belongingto frequency bands of 800 MHz, 1.5 GHz, and 1.9 GHz are currently used.Portable telephones using medium-earth-orbit and low-earth-orbitsatellites have been proposed by communications system companies inrecent years, and for such mobile satellite communication, the followingfrequency band allocation systems has been schemed. One system allocatesa frequency band of 1.6 GHz for uplink communication from portabletelephones on the ground to satellites and a frequency band of 2.4 GHzfor downlink communication from satellites to portable telephones on theground. Another system allocates a frequency band of 1.6 GHz for bothuplink and downlink communications. For such communication, circularpolarization is generally used to guarantee the quality of radiocommunication lines.

Proposed as an exemplary antenna construction is, as shown in FIG. 7, afolding antenna array 25 (see “Non-geostationary geostationary SatelliteCommunication Systems of the World”, ITU Research, No. 261/262, NewJapan ITU Society, August 1993, p. 36). The folding antenna array 25uses a transmitting microstrip flat antenna (hereinafter referred to asthe “transmitting flat antenna) 22 and a receiving microstrip flatantenna (hereinafter referred to as the “receiving flat antenna) 23 forsatellite communication.

The folding antenna array 25 will be described. For the sake ofexplanation, a construction proposed by the ODYSSEY system (TRW Corp. ofthe U.S) that is disclosed in the aforementioned literature “ITUResearch” will be taken as an example. A portable telephone 92 shown inFIG. 7 has the folding antenna array 25 that has the transmitting flatantenna 22 and the receiving flat antenna 23 arranged on a dielectric.The folding antenna array 25 can be arbitrarily folded with respect tothe portable telephone 92 at a folding angle α ranging from 0 to 180°through hinges 85.

In this case, the transmitting flat antenna 22 and the receiving flatantenna 23 communicate with a satellite using frequencies f1, f2,respectively. In the case of a satellite communication system using thesame frequency f1 for both transmission and reception, only thetransmitting flat antenna 22 can be used for both transmission andreception. Generally, the frequency f1 uses a frequency band of 1.6 GHzand the frequency f2 uses a frequency band of 2.4 GHz.

However, a small-sized flat antenna using a dielectric sheet has anarrow bandwidth, and the resonance frequency of the flat antenna variesdue to interference between itself and surrounding dielectrics such as ahousing and a human body. As a results the transmission efficiency andreception sensitivity of the antenna have been impaired. Especially, inthe case of communicating with a low-earth-orbit satellite, loss inantenna gain caused by the head of a human body is addressed as aproblem.

Further, communication sensitivity at low elevation angles is lost inthe flat antenna when the main beam is directed toward the zenith (at anelevation angle of 90°). While the use of either the flat antenna or thehelical antenna has been proposed in mobile communication through acommunications satellite, satisfactory communication sensitivity can beobtained only either when the satellite is at low elevation angles orwhen the satellite is at high elevation angles due to restrictions onthe directivity specific to each type of antenna.

The present invention has been made to overcome the aforementionedproblem by preventing the nearing of an antenna element toward a humanbody (especially, the head) when the user uses a portable radiocommunication device. That is, in a circularly polarized antenna that ismounted on a portable radio communication device, a communicatingsection is arranged between the portable radio communication device andthe antenna element.

Further, the present invention is characterized as providing twocircularly polarized antennas on a portable radio communication device,and the main beam radiating direction of one of these antennas is madedifferent from that of the other.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrative of a portable radio communicationdevice, which is an of embodiment of the present invention;

FIG. 2 is a diagram showing a condition in which radiation from anantenna is not shielded by the head of a human body through the use of aportable telephone, which is the embodiment of the present invention;

FIG. 3A is a diagram illustrative of an antenna having a communicatingsection in a four-wire helical antenna

FIG. 3B is a diagram illustrative of an antenna having a communicatingsection in a monofilar helical antenna;

FIG. 4 is a diagram showing another embodiment of the present invention,in which a portable radio communication device has a flat antenna meansand a helical antenna means mounted thereon;

FIG. 5 is a block diagram showing the antenna circuit for the helicalantenna means and the flat antenna means;

FIG. 6A shows the relative power of the main beams of circularlypolarized waves of the flat antenNa;

FIG. 6B shows the relative power of the main beams of circularlypolarized waves of the helical antenna;

FIG. 6C shows the relative power of the synthesized main beams of FIGS.6A and 6B;

FIG. 7 is a diagram illustrative of a conventional portable radiocommunication device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an embodiment of the present invention. Reference numeral 5denotes a communicating section constructed of a coaxial line or amicrostrip line. A circularly polarized helical antenna 14 constructedof a coaxial line 9 and the like is separated from a portable telephone92 by the communicating section 5. It may be noted that referencenumeral 81 denotes a display section; 82, a receiver; 83, an operatingsection; and 84, a transmitter.

First, the operation and characteristics of the helical antenna 14 thatgenerates circularly polarized waves for satellite communication will bedescribed. As the helical antenna 14, for example, a two-wire helicalantenna (disclosed in Unexamined Japanese Patent Publication 3-274904)and the like are known. This two-wire helical antenna is employed in thepresent embodiment. The helical antenna 14 includes: the coaxial line 9serving as a radiating element and a conductor 8, electrically couplesthe core conductor of the coaxial line 9 serving as the radiatingelement and the conductor 8 at a feed point 7, and electrically couplesan outer conductor of the coaxial line 9 serving as the radiatingelement and the conductor 8 at the helix end 6. Reference numeral 11denotes a dielectric cylinder, around which the coaxial line 9 and theconductor 8 are wound spirally.

The operation will be described based on high frequency current flowingthrough the helical antenna 14. The feed point 7 of the helical antenna14 is located on top of the antenna. Nothing serving as an antennaelement is connected to the outer conductor-of the coaxial line 9serving as the radiating element. When high frequency current exitingfrom the core conductor of the coaxial line 9 at the feed point 7 isflowing upward from the helix end 6 on the outer wall side of the outerconductor of the coaxial line 9, current is flowing in an oppositedirection on the inner wall side of the outer conductor of the coaxialline 9. Therefore, in nominal terms, no high frequency current isflowing on the outer conductor of the coaxial line 9. As a result, thehigh frequency current becomes a loop current. Since the conductor 8 andthe coaxial line 9 are wound around the dielectric cylinder 11 spirally,the high frequency current produces an electric field along the helicesand radiates circular polarization.

Then, during the operation of connecting the helical antenna 14 to theportable telephone 92, when the radiating element approaches thetelephone housing, radiation pattern is disturbed. As a result, theperformance of the antenna as an independent body is impaired, which inturn requires that the operation of matching the electromagneticcharacteristics of both the housing and the antenna be performed. Thisoperation impairs productivity. Further, the radiating element of theantenna nearing the telephone housing comes closer also to the head of ahuman body, and this makes it hard for the antenna to perform what it isexpected to do. To overcome this problem, the communicating section 5 isarranged in an antenna holder 10 so that the antenna can perform what itis expected to do by reducing interference between the helical antenna14 and the telephone housing. A sliding connector 13 is arranged on theupper right side surface of the portable telephone 92, and a slidingconnector 12 is arranged on the side surface of the communicatingsection 5, so that the antenna holder 10 is releasable. The length ofthe communicating section 5 is designed to be about 20 to 100% of thephysical length of the radiating element of the circularly polarizedantenna, or to be about 0.1 to 0.5λ (wavelength) of the operatingwavelength of the radiating element of the circularly polarized antenna.

Since the communicating section 5 is arranged in the antenna holder 10,the distance between the telephone housing and the helical antenna 14,and the distance between the head of a human body and the helicalantenna 14 can be increased, which in turn allows appropriate antennaperformance to be maintained. FIG. 2 shows a condition in whichradiation from the antenna is not shielded by the head of a human bodythrough the use of a portable telephone according to the presentembodiment. It is understood from this drawing that antenna gain at lowelevation angles necessary for communication with satellites in lowearth orbit is not lost.

While a two-wire helical antenna is employed in the aforementionedembodiment, other types of helical antennas may be employed as well. Forexample, a four-wire helical antenna 15 having four conductors as aradiating element such as shown in FIG. 3A, a monofilar (one-wire)helical antenna constructed of a ground plane 17 and a conductor 16 suchas shown in FIG. 3B, and the like can provide similar advantages as longas the communicating section 5 is arranged in the antenna holder 10.

It may be noted that an optimal type of helical antenna may be selectedin accordance with the system in which a portable radio communicationdevice is used. The helical antenna may be a rotating type or a pull-outtype so that the helical antenna may be received in the housing of theradio communication device.

Further, while a coaxial line or a microstrip line is accommodated inthe communicating section 5 arranged in the antenna holder 10 in theaforementioned example, the present invention is limited to thisexample, but may be applied to a case where the communicating section 5is constructed of a coaxial line, a microstrip line, or the like.Further, while the antenna is designed to be releasable through thesliding connector 13 and the sliding connector 12, the present inventionis not-limited to this design, but may be applied to a fixed antennadesign as long as the communicating section 5 is provided.

FIG. 4 shows another embodiment of the present invention. Partscorresponding to the embodiment shown in FIGS. 1 to 3 are assigned tothe same reference numeral, and detailed description is omitted here. InFIG. 4, reference numeral 40 denotes a flat antenna means; 14, a helicalantenna means; and 92, a portable radio communication device (portabletelephone). The flat antenna means 40 is arranged on an upper surfaceportion of the housing of the potable radio communication device 92, andthe helical antenna means 14 is arranged on an upper side surfaceportion of the housing so as to extend upward. FIG. 5 is a block diagramshowing a circuit of the antennas. A signal synthesizer 32 is connectedto a radio communication section 31. A signal selector may be used inplace of the signal synthesizer 32. Both antennas have different mainbeam radiating directions, but have the same operating frequency bandand the same rotating direction of circular polarization.

The flat antenna means 40 is constructed so that a patch-like conductor2 is bonded onto the upper surface of a dielectric sheet 3 and that aground plane (not shown) is bonded onto the lower surface of thedielectric sheet 3. A through hole (not shown) is arranged in thedielectric sheet 3. A feed pin 1 is inserted into the through hole tothereby electrically connect the feed pin 1 to the patch-like conductor2. At this time, a conductor portion around the through hole is removedto prevent the feed pin 1 from contacting with the ground plane.Similarly, a through hole is arranged in a conductor plate 50, and it isarranged so that the conductor plate 50 does not come in electriccontact with the feed pin 1. The conductor plate 50 is slightly largerthan the flat antenna means 40 in size. The commonest shape of thepatch-like conductor 2 is substantially square. The patch-like conductor2 resonates at low frequencies in the direction of a long side and athigh frequencies in the direction of a short side. That is, thepatch-like conductor 2 resonates at two different frequencies, andoperates as a circularly polarized antenna between two differentfrequencies. Impedance matching is provided by adjusting the position ofthe feed pin 1.

The main beam of the flat antenna means 40 is generally directed towardthe zenith (FIG. 6A), and therefore degree of design freedom isrestricted (there is some degree of design freedom, depending on thesize of the conductor plate 50). On the other hand, a large degree ofdesign freedom is given to the helical antenna means 14. It is possibleto select winding conditions so that the main beam is directed at lowelevation angles (FIG. 6B). By combining these two types of directiveantennas and arranging them on the portable radio communication devicein such a manner as shown in FIG. 4, stable communication sensitivitycan be provided raging from a high elevation angle (toward the zenith)to a low elevation angle (FIG. 6C).

Further, the helical antenna means 14 shown in FIG. 1 is accommodatedand held in an antenna holding tube 10. The helical antenna means 14 isheld at a position that is distant from the upper portion of theportable radio communication device 92 while interposing a signaltransmission path (a coaxial line 4 or a microstrip line) between theportable radio communication device 92 and the helical antenna means 14,the signal transmission path being led from the radio communicationsection 31. Since the main beam of the helical antenna means (two-wirehelical antenna) 14 is directed at a low elevation angle, loss inantenna gain brought about by the head of a human body can be preventedby holding the helical antenna means 14 above the portable radiocommunication device 92 so as to be distant from the portable radiocommunication device 92.

While a square microstrip flat antenna has been exemplified as the flatantenna in the aforementioned embodiment, a triangular, pentagonal, orcircular microstrip antenna may also be used. Further, while one-pointback feeding has been exemplified as the feed system, any one oftwo-point back feeding, and one-point feeding or two-point feeding tothe peripheral of a patch may also be chosen. Still further, a spiralantenna may also be employed.

While a two-wire helical antenna has been exemplified as the helicalantenna, a four-wire helical antenna as shown in FIG. 3A, a monofilar(one-wire) helical antenna as shown in FIG. 3B, a three-wire helicalantenna, and the like may also be chosen in accordance with thecommunications satellite system.

Further, loss in the antenna gain of a flat antenna caused by the headof a human body may be prevented by arranging the flat antenna on thetop end portion of a helical antenna, which is fixed to the antennaholding tube. A signal transmission path is provided in the antennaholding tube to feed the signal to the flat antenna.

As described in the foregoing, the present invention is characterized asproviding a communicating section that transmits a signal between aportable radio communication device and a circularly polarized antennathat is arranged above the portable radio communication device. As aresult of this arrangement, not only satisfactory satellitecommunication is permitted, but also productivity can be improved.

Further, in a satellite communication system that requires satellitehandover (switching from one satellite to another) at low elevationangles, reliability in communications at low elevation angles can beimproved.

Independently of elevation angles of communications satellites as viewedfrom the ground, satisfactory communication sensitivity can be obtainedeasily. In addition, handover from a satellite at a high elevation angleto a satellite at a low elevation angle (and vice versa) can beimplemented smoothly.

What is claimed is:
 1. A portable radio communication device comprising:a communication section for transmitting a signal arranged at an upperportion of a housing of the radio communication device, the housingaccommodating a radio communication section therein; and a radiatingelement of a chokeless circularly polarized antenna held on thecommunication section such that the entire radiating element is heldaway from the housing, wherein the radiating element of the circularlypolarized antenna is a radiating element of an antenna having an antennagain at low elevation angles for communication with satellites in lowearth orbit, wherein a main beam of the circularly polarized antenna isdirected at a low elevation angle, and wherein the communication sectionholds the circularly polarized antenna at a height such that acommunication with a satellite at a low elevation angle is notsubstantially obstructed by a user's head.
 2. A portable radiocommunication device comprising: a communication section fortransmitting a signal arranged at an upper portion of a housing of theradio communication device, the housing accommodating a radiocommunication section therein; a radiating element of a first chokelesscircularly polarized antenna held on the communication section such thatthe entire radiating element is held away from the housing, wherein theradiating element of the circularly polarized antenna is a radiatingelement of an antenna having an antenna gain at low elevation angles forcommunication with satellites in low earth orbit, wherein a main beam ofthe first circularly polarized antenna is directed at a low elevationangle, and wherein the communication section holds the circularlypolarized antenna at a height such that a communication with a satelliteat a low elevation angle is not substantially obstructed by a user'shead; and a second chokeless circularly polarized antenna, wherein amain beam of the second circularly polarized antenna is directed at ahigh elevation angle.
 3. A portable communication device according toclaim 2, wherein the second circularly polarized antenna is a flatantenna and the first circularly polarized antenna is a helical atenna,a conductor surface of a patch of the flat antanna and a top end portionof the helical atenna being directed upward with respect to a housing ofthe radio communication device.
 4. A portable radio communication deviceaccording to claim 3, wherein the flat antenna is fixed to the top endportion of the helical atenna.
 5. A portable radio communication deviceaccording to claim 3, wherein the helical antenna is supported at theupper portion of the housing of the radio communication device so as tobe distant from the upper portion of the housing while interposing asignal transmission path between the helical antenna and the upperportion of the housing.